Fluoroformate process

It is noteworthy that the heretofore not accessible at acceptable cost diethyleneglycol bis-vinyl carbonate called CVD [see scheme 100] is made in 80% yield using the fluoroformate process as depicted in table 3-15. 

In our continuing trials to extent the scope of the vinylic carbonates synthesis through the fluoroformate process, vinyl menthyl carbonate was obtained in excellent yield (80%) from menthyl fluoroformate. The polymer of vinyl menthyl carbonate was also proposed as menthol-release agent. It is noteworthy that this polymer can be easily prepared by reaction of menthyl fluoroformate with poly(vinyl alcohol) in DM50. 

An alternative means of technical-scale access to fluoroarenes is the fluoroformate method. Starting from the corresponding phenol a fluoroformate is generated by reaction with carbonyl chloride fluoride and subsequently catalytically decarboxy-lated to the aryl fluoride, in the gas phase, by contact with hot platinum [80] (Scheme 2.30). A newer, greener variant of the fluoroformate process has recently been introduced by Rhodia. In this the fluoroformate is formed by the (catalyzed) reaction of the phenol with COj in HF, and the expensive platinum catalyst is replaced by an aluminum-based material. 

Depending on the ring substituent, trifluoromethoxyben2enes can be made by the sequential chlorination—fluorination of anisole(s) (351—354). A one-step process with commercial potential is the BF (or SbF2)-cataly2ed reaction of phenol with carbon tetrachloride/hydrogen fluoride (355). Aryl trifluoromethyl ethers, which may not be accessible by the above routes,may be made by fluorination of aryl fluoroformates or aryl chlorothioformates with sulfur tetrafluoride (348) or molybdenum hexafluoride (356). 

Many solvent properties are related to density and vary with pressure in a SCF. These include the dielectric constant (er), the Hildebrand parameter (S) and n [5], The amount a parameter varies with pressure is different for each substance. So, for example, for scC02, which is very nonpolar, there is very little variation in the dielectric constant with pressure. However, the dielectric constants of both water and fluoroform vary considerably with pressure (Figure 6.3). This variation leads to the concept of tunable solvent parameters. If a property shows a strong pressure dependence, then it is possible to tune the parameter to that required for a particular process simply by altering the pressure [6], This may be useful in selectively extracting natural products or even in varying the chemical potential of reactants and catalysts in a reaction to alter the rate or product distributions of the reaction. 

There are some reactions in which boron trifluoride and boron trifluoride-diethyl ether complex are used as fluorinating agents, but they are not so frequently used and widespread. The best-known reaction is the decomposition of fluoroformates. In this type of reaction boron trifluoride or pyridine are essentially required as catalysts for the decomposition process. The formation of fluoroformates is established4 5 and the decomposition proceeds cither by heating in pyridine at higher temperature6 or by addition of boron trifluoride-diethyl ether complex at 0-50°C.7... 

In the gas phase, the asymmetric CO stretch lifetime is 1.28 0.1 ns. The solvent can provide an alternative relaxation pathway that requires single phonon excitation (or phonon annihilation) (102) at 150 cm-1. Some support for this picture is provided by the results shown in Fig. 8. When Ar is the solvent at 3 mol/L, a single exponential decay is observed with a lifetime that is the same as the zero density lifetime, within experimental error. While Ar is effective at relaxing the low-frequency modes of W(CO)6, as discussed in conjunction with Fig. 8, it has no affect on the asymmetric CO stretch lifetime. The DOS of Ar cuts off at "-60 cm-1 (108). If the role of the solvent is to open a relaxation pathway involving intermolecular interactions that require the deposition of 150 cm-1 into the solvent, then in Ar the process would require the excitation of three phonons. A three-phonon process would be much less probable than single phonon processes that may occur in the polyatomic solvents. In this picture, the differences in the actual lifetimes measured in ethane, fluoroform, and CO2 (see Fig. 3) are attributed to differences in the phonon DOS at 150 cm-1 or to the magnitude of the coupling matrix elements. 

Aliphatic carbamates 6 have also been diazotized and subjected to Quorodediazoniation to yield the corresponding alkyl fluoroformates 7 (see Vol. ElOa, pp 729-731), which are useful as synthetic tools in the preparation of peptides and as intermediates in the preparation of alkyl fluorides. This preparation of alkyl fluoroformates from the readily available carbamates using hydrogen fluoridc/pyridine eliminates the need to employ phosgene or its derivatives in the synthetic process. ... 

Much better results can be obtained with substituted aromatics. The reaction of aryl chloro- or fluoroformates which have alkyl groups in position 2 and 6 gives fluoroaromalic compounds in good yield. The Friedel-Crafts reaction is widely suppressed although Lewis acids or hydrogen fluoride are present in the reaction mixture. Another advantage of this process is that the fluoroaromalic compounds can be obtained from the fluoro- as well as from the chloroformates. which, in general, are easier to prepare, A typical example is the formation of 2-fluoro-1.3-dimethylbenzene (2). ... 

The process and mechanism for nucleophilic transfer from MesSiCFs to electrophilic sites are analogous to the clever use of DMF as a reservoir for trifluoromethide (10.45A), formed by reaction of fluoroform with a base [96], in a process outlined in Figure 10.45 they are also analogous to the use of iodoperfluoroalkanes with tetrakis(dimethylami-no)ethene [99] (Figure 10.46). 

Aliphatic or alicyclic fluoroformates may be prepared continuously from the reaction of the corresponding alcohols with a mixture of carbonyl halides e.g. COFj, COCIF and COClj at -20 to +80 "C in the presence of isobutene, which acts as a hydrogen halide acceptor). The process was illustrated using methanol, t-butanol and cyclohexanol as examples [1118]. 

Therefore, much effort has been devoted to the research of new industrializable routes to fluorinated aromatics derivatives which are as far as possible versatile and without the drawbacks of classical processes. Among the reported reactions (refs. 4-7) aryl fluoroformate decarboxylation seems to be very attractive. Aryl fluoroformates are easily prepared from the corresponding phenol, phosgene and anhydrous hydrogen fluoride, which are widely available and cheap raw materials. 

Abstract - This work is concerned with the origin of effects on rate equilibrium processes when reactions are performed in dipolar aprotic media such as dimethyl sulfoxide and dimethyl-formamide compared to typical hydroxylic media. An example of processes studied in our laboratory is the competition between proton abstraction and a-complex (Meisenheimer adduct) formation in the interaction of nitroaromatic compounds with basic systems (e.g. 1,3-dinitrobenzene in DMF-D20-Na0D). Other reactions studied are the base catalyzed isotopic exchange of D2 in aqueous DMSO mixtures, and also isotopic exchange of fluoroform. It has been found possible in certain cases to dissect the initial state and transition state contributions to the reaction rates from the kinetically measured enthalpies of activation and the thermodynamically evaluated enthalpies of transfer of the reactants. This procedure affords insight into transition state properties and behaviour. 

Sodium trifluoroacetate, in the presence of copper(l) iodide, was also used as trifluoromethyl source to replace halogen by trifluoromelhyl group in the thiophene system. Sodium trifluoroacetate was decarboxylated, forming fluoroform, when heated alone in aqueous N-methylpyrrolidin-2-one. The addition of copper(l) iodide increased the rate of decarboxylation dramatically. The mechanism of this process was explored and an intermediate [CFsCul] was proposed. Introduction of higher perfluoroalkyl groups from their corresponding sodium perfluoroalkane carboxyl-ates was also shown to be possible [58],... 

---